This process is performed by warming, anaerobic digestion(fermentation), ultrafiltration, and finally reversed osmotic separation steps also, the concentrated solution rejected by RO separation being possibly used as liquid fertilizer.
Generally, many known methods for waste water treatment have some problems in economical and technical point of view, so few of them have been used in industrial fields. Although the self-purification limit is known to be 10 mg/l of BOD, the effluents from domestic waste water range from tens to thousands mg/l of BOD and tens to ten thousands in animal waste water.